Immediate contact reactions (contact urticaria) can occur after skin contact with a wide range of substances. We studied the incidence of immediate contact reactions (wheal and flare) to the European standard series allergens in 664 patients. Patch tests were first examined at 30 min for immediate patch test (IPT) reactions, and again at D2 and D4 for delayed patch test (DPT) reactions. Almost all the allergens of the European standard series caused IPT reactions. IPT reactions were most commonly seen with Myroxylon Pereirae (balsam of Peru) (113 reactions), fragrance mix (112 reactions), paraben mix (30 reactions) and clioquinol (13 reactions); these reactions were followed by DPT reactions to the same substance in 13.4%, 8.8%, 10% and 7.7%, respectively. For certain substances, patients with (+) IPT reactions had a significantly higher incidence of DPT reactions to the same allergen, as compared to patients with (-) IPT reactions (fragrance compounds p<0.001, formaldehyde p<0.005, thiuram mix p<0.01, paraben mix p<0.05). Thus, perhaps the mechanisms involved in IPT reactions are not the same for all substances. At least for certain substances, an IPT reaction may be related to the development of a DPT reaction.